1. Field of the Invention
The present invention relates to a film carrier that is used for TAB mounting of electronic devices such as semiconductor devices, to a method of transferring conductive patters to correct positions, and to masks to be used therefor.
2. Discussion of the Related Art
When electronic devices, such as, semiconductor devices, are mounted with TAB (Tape Automated bonding), a film carrier is used as a base substrate. One example of a film carrier is shown in FIG. 1.
A film carrier has an insulation film 2 as a base substrate material, a conductor pattern 8 provided on the film, and an aperture 6 provided at a position separated a predetermined distance from each of both edges of the film 2. The aperture 6 shown in FIG. 1 is positioned generally at the center of the tape in its width direction (a direction perpendicular to the transfer direction). The film 2 has index perforation holes (which are also called sprocket holes, and hereinafter referred to as "IP") 4 formed along both of the edges in the transfer direction. The IP 4 is used to control feeding of the film in a variety of transfer processes and used as references for position coordinates on the film, for example, in the manufacture of a film carrier wherein a conductor pattern is formed on the film, in the feeding or positioning steps in ILB (inner lead bonding) process, and the like. A part of the conductive pattern 8 protrudes into the aperture 6 (the protruded section is called an "inner lead"), wherein electronic devices such as semiconductor devices are electrically connected to the inner lead section. In other words, electrode sections of an electronic device are positioned within the aperture 6.
A conductive pattern 8 of a film carrier is typically manufactured by the following steps as shown in FIGS. 2(a)-2(g).
(1) A first step of adhering a conductor layer 5 of a metal film such as a copper film (FIG. 2(b)) on a top surface of a film 2 that defines IP 4 and apertures 6 and that is coated with an adhesive (not shown) (FIG. 2(a)),
(2) A second step of coating photoresist 7 on the surface of the conductor layer 5 (FIG. 2(c)),
(3) A third step of performing exposure, using a mask 10 having a pattern for forming a conductor pattern, thereby printing the pattern for forming the conductor pattern on the photoresist 7,
(4) A fourth step of etching the structure wherein the photoresist 7 exposed in the third step remains on the conductor layer 5 (FIG. 2(e)) to form a predetermined conductor pattern, and then removing the photoresist, and
(5) A fifth step of plating the conductor pattern 8 of a film carrier in which the photoresist 7 has been removed (FIG. 2(f)) with tin or the like 12 as required (FIG. 2(g)).
In one embodiment, a protection resist is coated on the rear side of the conductor layer 5, the surface of the conductor layer 5 is etched, and the photoresist 7 and the protection resist are removed.
Referring also to FIG. 3, in the third step in which the photoresist 7 is exposed, using the mask, the following method is often used. A conductor pattern forming pattern 102 representing the shape of the conductor pattern 8 to be exposed is drawn on a glass mask 10. Using this mask, the conductor pattern forming pattern drawn on the mask is exposed on the photoresist 7 of the film carrier, using a lens 13 of, for example, the magnification of 1 to 1 or 1 to 2, developed and fixed, and etching is performed to form the conductor pattern 8.
Connecting sections of the conductor pattern 8, i.e., inner leads, to be connected to an electronic device protrude into the aperture 6, and the inner leads of the conductor pattern 8 are connected to electrodes of an electronic device within the aperture 6. Therefore, considering the position of the electronic device while it is connected and after it has been connected, positioning of the conductor pattern 8 and the aperture 6 is also required. It is noted that the apertures 6 can be formed in the film carrier with high precision by a conventional technique, using the IP reference line as a reference.
The conductor pattern 8 has rod-shaped sections extending from the film into the aperture 6 so that an electronic device is connected thereto. Therefore, if the position of the conductor pattern is deviated from the IP reference coordinates 24 (X axis), 26 (Y axis), when an electronic device is connected to the conductor pattern, the rod-shaped extended conductor sections may be bent, resulting in faulty connection, cutting of the circuit or short-circuit, or the conductor sections may not be connected to an electronic device. Accordingly, the electronic device may break down.
Deviations of the conductor pattern with respect to the IP reference coordinates 24, 26 are defined by three different deviations, namely, X-direction deviation in a direction of the length of the film, Y-direction deviation in a direction perpendicular thereto, and a rotational deviation. If the three deviations can be detected prior to the full transfer forming, the position of the mask on an exposure apparatus (not shown) can be adjusted to dispose the conductor pattern forming pattern at the correct position on the film carrier, namely, at the correct position that is calculated and designed, and then the pattern is exposed.
To detect deviations of the position of the conductor pattern, in other words, deviations of the conductor pattern from its correct position on the film carrier, the following method has been used.
(1) When a film carrier is preliminarily exposed, developed and fixed, a conductor pattern is observed on a conductor layer. By using IP reference coordinates 24, 26 shown in FIG. 1 as references, a relative position of a conductor pattern 8 transferred by the use of a projector is measured. Based on the measured value, deviations of the conductor pattern from the designed position are detected, so that the position of the mask on the exposure apparatus is adjusted.
However, according to this method, the designed position of the conductor pattern and the preliminarily formed position are superposed and projected. Since deviations at different areas of the conductor pattern are different from one another, it is difficult to obtain the above-described three types of deviations in one lot. As a result, the number of required positional corrections increases.
(2) Japanese Laid-open patent application SHO 59-88859 describes a method in which a metal foil film carrier is used as a film carrier, wherein both of an IP pattern and a conductor pattern forming pattern are drawn on a mask, these patterns are transferred on the metal foil and then the IPs are perforated. This method is not applicable when a film carrier has IPs formed in advance.
(3) Japanese Laid-open patent application SHO 62-234337 describes a method in which "+" marks for positioning are drawn on a mask, the marks are transferred to a film carrier, and an electric device is positioned based on the marks. In accordance with this method, even if the conductor pattern is deviated from the IP reference coordinates, the electric device can be correctly disposed with respect to the conductor pattern. However, this method cannot be used for correcting deviations of the conductor pattern from the IP reference coordinates. Also, a line used in the "+" mark has a certain thickness, resulting in the lowered positioning accuracy.